The weight thing is such a problem with kids. My daughter eats everything that I can get her to eat, and by their charts, she is 4 pounds underweight. However, she looks, body wise, just like I did at her age, and she's super active and muscular. Luckily, my Pediatrician is not concerned at this point and sees her as being "healthy".
Does your daughter resemble you or your husband at that age? If so, did the person that she resembles grow out of the "little pot belly"? If so, then don't worry about it. If not, and one of you have battled with weight, then you might want to consider having different eating habits for her that will help her manage later on in life.
From what I have seen, it looks like there is a huge increase in childhood obesity which is leading to an increase in diabetes. Your pediatrician is probably just trying to find out if there is a reason to be concerned at this point.